COG dielectric with high K

ABSTRACT

A composition consisting essentially of 60.0-70.0 mol % TiO 2 , 14.3-20.0 mol % Nd 2  O 3 , 11.0-16.7 mol % BaO, 1.0-8.0 mol % ZrO 2  and 0.05-0.30 mol % CeO 2 . This composition is useful for forming densified ceramic dielectric bodies having a dielectric constant of at least 65 and which meet COG specifications, and multilayer capacitors that contain such dielectric bodies.

FIELD OF THE INVENTION

The invention is related to a dielectric composition. More particularly,the invention is related to a dielectric composition with goodtemperature stability and high dielectric constant, for use inmultilayer devices such as capacitors.

BACKGROUND OF THE INVENTION

Barium-neodymium-titanate has been widely used a basis for multilayercapacitor (MLC) dielectrics with COG temperature dependence since 1968,when Bolton and Muhlstadt at the University of Illinois (Ph.D and M.S.Thesis, respectively) discovered that this material combined arelatively high dielectric constant with good temperature stability.Since then, various workers have attempted to identify the compositionof the primary phase in this material, with little agreement. Suggestedcompositions, and the date of publication, are summarized below:

    ______________________________________                                                                Mol %                                                                  BaO    Nd.sub.2 O.sub.3                                                                      TiO.sub.2                                     ______________________________________                                        BaO.Nd.sub.2 O.sub.3.3TiO.sub.2 (1981)                                                           20.0     20.0    60.0                                      BaO.Nd.sub.2 O.sub.3.5TiO.sub.2 (1981)                                                           14.3     14.3    71.4                                      BaO.Nd.sub.2 O.sub.3.4TiO.sub.2 (1984)                                                           16.7     16.7    66.7                                      15BaO.19Nd.sub.2 O.sub.3.72TiO.sub.2 (1984)                                                      14.2     17.9    67.9                                      4BaO.5Nd.sub.2 O.sub.3.18TiO.sub.2 (1986)                                                        14.8     18.5    66.7                                      ______________________________________                                    

Part of the difficulty in obtaining agreement is that thebarium-neodymium-titanate was made by calcining a mechanical mixture ofpowdered ingredients. Generally, the neodymium oxide that is availablecommercially has a particle size greater than 10 microns and isdifficult to mill to a fine powder, so the degree of reaction with theother ingredients can be variable. One would expect that this problemcould be minimized if the compound were made by chemical synthesis, forexample by the method described by Colombet and Magnier in U.S. Pat. No.4,757,037 which issued in 1988. In the work of Colombet and Magnier, abarium-neodymium-titanate of nominal composition BaO. Nd₂ O₃.3TiO₂ wasreported to have been made by co-precipitation, after mixing a solutionof barium and neodymium nitrates with a titania sol. However, thiscomposition lacked the required temperature stability.

It is usually not possible to achieve the requisite temperaturestability with the barium-neodymium-titanate system unless thecomposition is modified with additives. For example, Kashima and Tomuro,in U.S. Pat. No. 4,522,927 which issued in 1985, describe changes in theTemperature Coefficient of Capacitance (TCC) produced by replacingtitanium oxide with zirconium oxide according to the formula:

    xBaO--yNd.sub.2 O.sub.3 --z(Ti.sub.1-m Zr.sub.m)O.sub.2

where x+y+z=1.00, and 0.05<m<0.25. Small additions of MnO₂, Cr₂ O₃, FeO,NiO or CoO are also suggested. Despite the beneficial effect on TCC ofreplacing some titanium oxide with zirconium oxide, the compositionsdisclosed by Kashima and Tomuro was found to yield dielectrics with lowinsulation resistance at 125° C.

Numerous other modifications to the barium-neodymium-titanate system aredescribed in the prior art but they typically involve the use of bismuthoxide and/or lead oxide. (See, for example, U.S. Pat. No. 4,866,017).Bismuth oxide can react adversely with Pd electrodes in MLC's, and theprocessing of powders containing lead oxide can introduce health andenvironmental concerns. Partial substitution of neodymium oxide withsamarium oxide (Sm₂ O₃) or praseodymium oxide (Pr₆ O₁₁) has also beensuggested as a means of adjusting the TCC (e.g., U.S. Pat. No.4,500,942).

PRIOR ART U.S. Pat. No. 4,866,017 (Okawa)

Compositions are described in the system xBaO.yNd₂ O₃.zTiO₂.wBi₂ O₃ with0.141<x<0.157, 0.141<y<0.157, 0.656<z<0.663, and 0.025<w<0.060.

U.S. Pat. No. 4,757,037 (Columbet et al)

Fine powders of neodymium titanate or barium-neodymium-titanate aredisclosed. These powders are formed by mixing a solution of neodymiumnitrate or a solution of barium and neodymium nitrates with a sol oftitania particles having a size from about 10 to about 100 Angstroms indiameter, at a low pH. The co-precipitated powder is calcined at atemperature between 800° and 1300° C.

U.S. Pat. No. 4,753,906 (Nishigaki et al)

Compositions are disclosed of the form xBaO.yTiO₂.zR₂ O₃ where R isselected from Nd, Sm and La. Ba is partially replaced with ions selectedfrom the group consisting Sr, Ca and Mg. The dielectric compositions mayfurther contain oxides selected from the group consisting of Cr₂ O₃, Fe₂O₃, WO₃, SnO₂ and ZrO₂.

U.S. Pat. No. 4,713,726 (Sasazawa)

Dielectric ceramic compositions are described comprising a mixture of7-25 mol % BaTiO₃, 0.1-15 mol % Bi₂ O₃, 50-65 mol % TiO₂, 0.1-5 mol %LaO_(3/2) and 15-45 mol % NdO_(3/2) in a total of 100 mol %. Alsoincluded is at least one member selected from the group consisting of Y₂O₃, Gd₂ O₃ and CeO₂, and at least one member selected from the groupconsisting of Cr₂ O₃, MnO₂, NiO and CoO, in amounts of from 0.1 to 5.0parts by weight and from 0.01 to 1.0 parts by weight per 100 parts byweight of the mixture, respectively.

U.S. Pat. No. 4,522,927 (Kashima)

Dielectric compositions are disclosed represented by the formulaxBaO.yNd₂ O₃.z(Ti_(1-m) Zr_(m))O₂ wherein x+y+z=1.00 and m is between0.05 and 0.25. At least one member selected from the group MnO₂, Cr₂ O₃,FeO, NiO and CoO is added in the amount of 0.05 to 1.00% by weight ofthe total weight of the main components.

U.S. Pat. No. 4,500,942 (Wilson)

Compositions for NPO class capacitors are disclosed comprising a mixtureof BaO, PbO, Nd₂ O₃, Bi₂ O₃, TiO₂ one of the rare earth oxides selectedfrom the group consisting of Pr₆ O₁₁ and Sm₂ O₃.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a dielectric compositionfree of bismuth, lead and cadmium which can be fired into a denseceramic body with a dielectric constant (K) of at least 65.

It is another object of the invention to provide a ceramic compositionwhich can meet or exceed the Electrical Industries Association (EIA)specification of COG, sometimes known as NPO:

(1) a temperature coefficient of capacitance (TCC) of not more that+/-30 parts per million per ° C., with respect to the value at 25° C.,over the temperature range -55° to 125° C.;

(2) a dissipation factor (DF) of less than 0.1% at 25° C. when measuredat 1 KHz with 1.0 V(rms) applied;

(3) an insulation resistance (IR) of at least 1000 ohm.farads measuredat 25° C., and at least 100 ohm.farads when measured at 125° C.

In its primary aspect, the invention is directed to a composition forforming a densified ceramic dielectric body having the abovecharacteristics, the composition consisting essentially of:

(a) 60.0-70.0 mol % TiO₂

(b) 14.3-20.0 mol % Nd₂ O₃

(c) 11.0-16.7 mol % BaO

(d) 1.0-8.0 mol % ZrO₂ and

(e) 0.05-0.30 mol % CeO₂.

The invention is also directed to a dispersion of the above-describedcomposition in an organic medium which can be cast as a dielectricsheet.

In another aspect, the invention is directed to a dielectric layer madeby firing the above-described dielectric sheet to volatilize the organicmedium therefrom and to densify the inorganic solids by sintering.

In a further aspect, the invention is directed to a capacitor comprisinga plurality of the above-described dielectric layers interspersed withat least two metal electrode layers.

In a still further aspect, the invention is directed to a process forpreparing the above-described composition by co-precipitation andcalcination.

DETAILED DESCRIPTION OF THE INVENTION

The compositions of the invention can be made by mechanically mixingfinely divided powders of each ingredient by conventional means.Alternatively, the compositions can be prepared using neodymium titanatethat is made by a liquid-mix process of the invention which compriseschemical co-precipitation then calcination. Preferably, the compositionis prepared entirely by chemical co-precipitation and subsequentcalcination.

In the mechanical mix process, a mixture of finely divided powders ofbarium titanate, neodymium titanate, titanium oxide, zirconium oxide,and cerium oxide are used. The average particle size of each powdershould be about 1 mm or less, preferably 0.5 to 1.0 mm. Powders of theappropriate size are readily available commercially, except forneodymium titanate. Neodymium titanate (Nd₂ Ti₂ O₇) can be prepared bycalcining at about 1100° C. an intimate mixture of neodymium oxide andtitanium oxide powders, or precursors. However, as mentioned above, apreferred approach is to use a liquid-mix technique.

The liquid-mix method for preparing neodymium titanate can begin withthe step of preparing a solution of metal chelates by first mixing achelating agent with a solvent. The desired metal compounds are added bystirring and are of the general formula, MX_(n), wherein M is titaniumand neodymium, and X is an anion or a radical selected from HCO₂ --, CH₃CO₂ --, ⁻ OH, ⁻ OR, ⁻ NO₃ and ⁻ Cl and mixtures thereof, R being analkyl group; and n is 3 or 4 depending on the valence state of the metalcation M^(+n). Upon adjustment of the pH in the range of about 5 to 10,the chelating agent is capable of forming soluble metal chelates withthe metal cations.

The term chelating agent, as described by Cotton and Wilkinson inAdvanced Inorganic Chemistry (1962), is incorporated herein to refer to"a polydentate ligand whose structures permit the attachment of two ormore donor sites to the same metal ion simultaneously, thus closing oneor more rings. A ligand is defined as any atom, ion, or molecule capableof functioning as a donor partner in one or more coordinate bonds".Chelating agents useful in practising the invention arealpha-hydroxycarboxylic acids, such as lactic, glycolic, malic andcitric acid or alpha-aminocarboxylic acids, such as ethylene diaminetetracetic acid (EDTA) and glycine. A solution of the chelating agent isprepared using a solvent, for example, deionized water or mixtures ofdeionized water with miscible solvents such as methanol, ethanol,isopropanol and acetic acid. The solvent may optionally contain smallamounts of wetting agents or surfactants to facilitate dissolution ofthe metal compounds. It is important that a sufficient amount ofchelating agent be added to produce a clear solution of metal chelates.The desired metal compounds are added to the above chelating agent andsolvent by stirring. The pH is adjusted to a value in the range 5 to 10,typically by the addition of a base selected from ammonium hydroxide,tetramethylammonium hydroxide, sodium hydroxide, and potassiumhydroxide.

The metal chelate solution, prepared as described above, is mixed withan aqueous solution of a strong base such as, for example, sodiumhydroxide, potassium hydroxide, or lithium hydroxide in a highturbulence energy environment as described in co-pending, commonlyassigned application, U.S. Ser. No. 07/144,835 and passed, almostsimultaneously, to a receiving vessel (known as drown-out vessel). Thedesired high turbulence energy environment for mixing the metal chelatesolution stream and the aqueous basic solution stream can be achievedusing a mixing pump, mixing tee or by pumping the ingredient streamsthrough a coaxial jet mixer. Mixing may optionally be accomplished inthe presence of a surfactant, such as, for example, Igepal® CO-890, anethoxylated alkylphenol surfactant manufactured by GAF Corporation, NewYork, N.Y. The strong base increases the pH of the mixture to a valueabove 11 and induces precipitation of the reaction product, which isheated at about 100° C. for several hours to complete the decompositionof the metal chelates. The precipitate is recovered by filtering,washing to remove impurities, and then drying. The dried precipitate isgranulated and then calcined at 900° to 1100° C. to crystallize thepowder and to reduce the surface area from about 300 M² /gm to less than10 M² /gm.

A particularly preferred method of making the composition of theinvention is to form the entire composition by a liquid mix technique. Aco-precipitated barium-neodymium titanate with added dopants can beprepared by the method described above for neodymium titanate, exceptthat MX_(n) now includes other M cation such as zirconium and cerium inaddition to neodymium and titanium, and the aforementioned aqueoussolution of strong base contains barium ions. The barium ions areintroduced from water-soluble barium salts selected from the hydroxide,chloride, nitrate, and acetate. If barium hydroxide is used, pH can beadjusted to a value above about 11 by using a small excess of bariumhydroxide over the amount needed for stoichiometry in the precipitatedproduct, instead of using an alkali metal hydroxide.

The modified barium neodymium titanate composition of this invention canbe formulated into a dielectric green sheet. One method for forming suchsheet comprises casting a dispersion of the ceramic modified bariumneodymium titanate composition in a solution of polymeric binder andvolatile organic solvent onto a flexible substrate, such as a steel beltor polymeric film, and then heating the cast layer to remove thevolatile solvent therefrom.

The organic medium in which the ceramic solids are dispersed consists ofthe polymeric binder which is dissolved in a volatile organic solventand, optionally, other dissolved materials such as plasticizers, releaseagents, dispersing agents, stripping agents, antifouling agents andwetting agents.

To obtain better binding efficiency, it is preferred to use at least 5%wt. polymer binder for 95% wt. ceramic solids. However, it is furtherpreferred to use no more than 20% wt. polymer binder in 80% wt. ceramicsolids. Within these limits, it is desirable to use the least possibleamount of binder vis-a-vis solids in order to reduce the amount oforganics which must be removed by pyrolysis.

In the past, various polymeric materials have been employed as thebinder for green sheets, e.g., (poly)vinyl butyral, (poly)vinyl acetate,(poly)vinyl alcohol, cellulosic polymers such as methyl cellulose, ethylcellulose, hydroxyethyl cellulose, methylhydroxy-ethyl cellulose,atactic polypropylene, polyethylene, silicon polymers such as(poly)methyl siloxane, (poly)methylphenyl siloxane, polystyrene,butadiene/styrene copolymer, polystyrene, (poly)vinyl pyrrolidone,polyamides, high molecular weight polyethers, copolymers of ethyleneoxide and propylene oxide, polyacrylamides, and various acrylic polymerssuch as sodium polyacrylate, (poly)lower alkyl acrylates, (poly)loweralkyl methacrylates and various copolymers and multipolymers of loweralkyl acrylates and methacrylates. Copolymers of ethyl methacrylate andmethyl acrylate and terpolymers of ethyl acrylate, methyl methacrylateand methacrylic acid have been previously used as binders for slipcasting materials.

More recently, Usala, in U.S. Pat. No. 4,613,648 has disclosed anorganic binder which is a mixture of compatible multipolymers of 0-100%wt. C₁₋₈ alkyl methacrylate, 100-0% wt. C₁₋₈ alkyl acrylate and 0-5% wt.ethylenically unsaturated carboxylic acid or amine. Because the polymerspermit the use of minimum amounts of binder and maximum amounts ofdielectric solids, their use is preferred with the dielectriccomposition of this invention.

The solvent component of the casting solution is chosen so as to obtaincomplete solution of the polymer and sufficiently high volatility toenable the solvent to be evaporated from the dispersion by theapplication of relatively low levels of heat at atmospheric pressure. Inaddition, the solvent must boil well below the boiling point anddecomposition temperature of any other additives contained in theorganic medium. Thus, solvents having atmospheric boiling points below150° C. are used most frequently. Such solvents include acetone, xylene,methanol, ethanol, methyl ethyl ketone, 1,1,1-trichloroethane,tetrachloroethylene, amyl acetate, 2,2,4-triethylpentandiol-1,3-monoisobutyrate, toluene and methylene chloride.

Frequently, the organic medium will also contain a small amount,relative to the binder polymer, of a plasticizer which serves to lowerthe glass transition temperature (Tg) of the binder polymer. However,the use of such materials should be minimized in order to reduce theamount of organic materials which must be removed when the films casttherefrom are fired. The choice of plasticizers is, of course,determined primarily by the polymer which must be modified. Among theplasticizers which have been used in various binder systems are diethylphthalate, dibutyl phthalate, octyl phthalate, butyl benzyl phthalate,alkyl phosphates, polyalkylene glycols, glycerol, (poly)ethylene oxides,hydroxyethylated alkyl phenol, dialkyldithiophosphonate and(poly)isobutylene. Butyl benzyl phthalate is frequently used in acrylicpolymer systems because it can be used effectively in relatively smallconcentrations.

Multilayer devices such as circuits and capacitors can be fabricatedfrom green dielectric sheets and electrically conductive metallizations.For example, a metallization can be printed in the desired pattern upona green sheet. The printed sheets are stacked, laminated and cut to formthe desired structures. The green assemblage is then fired to effectremoval of the organic medium from the metallization material and of theorganic binder from the dielectric material. The removal of thesematerials is accomplished by a combination of evaporation and thermaldecomposition during the firing operation. In some instances, it mayalso be desirable to interpose a preliminary drying step prior tofiring. Conventionally, the thickness of an unfired dielectric sheet istypically about 18-30 microns and upon firing the thickness becomesabout 15-25 microns. The present invention, however, allows sheets ofthicknesses as small as 10 microns or less to be used.

The desired sintering temperature is determined by the physical andchemical characteristics of the dielectric material. Ordinarily thesintering temperature will be chosen to obtain maximum densification ofthe dielectric material. However, it will be recognized by those skilledin the art of fabricating electrical devices that maximum densificationis not always needed. Therefore, the term "sintering temperature" refersto the temperature (and implicity the amount of time as well) to obtainthe desired degree of densification of the dielectric material for theparticular application. The compositions of the invention sinter todense ceramic materials at a temperature of about 1240°-1320° C.

Sintering times also vary with the dielectric composition but ordinarilyabout 2.5 hours at the sintering temperature is preferred. Uponcompletion of sintering, the rate of cooling to ambient temperature iscarefully controlled in accordance with resistance of the compounds tothermal shock.

In one embodiment of the invention, modified barium neodymium titanatecompositions are formulated into dielectric sheets which are formed intomonolithic capacitors. A preferred method for forming such a monolithiccapacitor comprises the sequential steps of (1) forming a greendielectric sheet from the above-described composition and an organicbinder; (2) applying a layer of conductive electrode material dispersedin an organic medium to each of a plurality of the green sheets; (3)forming an assemblage of alternating layers of green sheets andelectrode material; and (4) firing the assemblage at a temperature above1240° C. to remove the organic medium and organic binder therefrom andto sinter the conductive electrode material and the dielectric material.A monolithic capacitor formed in this manner comprises a ceramicdielectric body having a dielectric constant of at least 65 and whichmeets COG specifications and at least two spaced metal electrodes incontact with the ceramic body.

EXAMPLES EXAMPLE 1

Neodymium titanate (Nd₂ O₃.2TiO₂) was prepared as follows. Neodymiumacetate tetrahydrate (169.7 g, 0.50 mole) and Tyzor®-LA (290.3 g, 0.50mole) were charged to a 500 ml flask under a nitrogen atmosphere.Tyzor®-LA is a 50% aqueous solution of the lactic acid ammonium salt ofchelated titanium manufactured by E.I. du Pont de Nemours and Co.,Wilmington, Del. ("Du Pont Co."). The charge was heated to reflux (99°C.) and maintained at reflux for about 30 mins. The temperature of theviolet-colored solution was then adjusted to 80°-85° C.

Into a 4100 ml polypropylene reactor was charged 2200 ml of de-ionizedwater. Carbon dioxide was removed from the water by sparging withnitrogen at about 70° C. for 1 hour. Potassium hydroxide pellets (258 g,87% KOH, 4.0 moles) were added to the hot de-gassed water and thetemperature of the charge adjusted to about 85° C.

By means of a peristaltic pump, an amount (about 6%) of the totalavailable potassium hydroxide was pumped through a jet mixer in advanceof the solution of neodymium acetate in Tyzor®-LA. The jet mixer used inthis preparation was a coaxial jet mixer like that described incopending, commonly assigned U.S. Application Ser. No. 07/144,835.Without interrupting the flow of the hot potassium hydroxide solution,the remainder of the potassium hydroxide solution was pumpedsimultaneously with the hot solution of neodymium acetate in Tyzor®-LAover about 1 minute through the jet mixer into a 4100 ml polypropylenereactor (drown-out vessel) containing 400 ml of de-ionized water and 5 gIgepal® CO-890. The drown-out vessel was equipped with an 11.5 cmcrescent-shaped Teflon® agitator blade, and the agitator speed was setat 445 rpm during the drown-out procedure. Teflon® is apolytetrafluoroethylene manufactured by the Du Pont Co.

The light blue slurry was heated under reflux (101° C.) for 4 hours.After cooling to about 25° C., the slurry was filtered and the filtercake washed with 16 liters of de-ionized water. It was then dried in avacuum oven (110°-120° C.) and ground to give 130.3 g of a light bluepowder with surface area of 276.4 M² /g. The composition calculated asmetal oxides was shown by inductively coupled plasma analysis (I.C.P.)to be as follows: 60.2% Nd₂ O₃, 30.2% TiO₂, and <0.01% K₂ O. Theoreticalamounts for Nd₂ Ti₂ O₇ are 67.82% Nd₂ O₃ and 32.2% TiO₂. The loss onignition (LOI) of a 3-5 gm sample of the powder heated at 1050° C. for 3hours was 10.03%. After the ignition loss test, the powder was found tobe crystalline neodymium titanate by X-ray diffraction.

This powder was calcined at 900° C. for 5 hours. A ceramic slurry wasprepared from 25.00 gms of neodymium titanate, 9.28 gms of bariumtitanate and 4.02 gms of titanium oxide in 26.0 gms of 1-1-1trichloroethane and 1.20 gms of AB1015 surfactant (Du Pont Co.). Thesurfactant used was a low molecular weight acrylic polymer in an organicsolvent. The barium titanate and titanium oxide powders had an averageparticle size less than 1 micron and they were blended with theneodymium titanate by milling in a ball mill with zirconia media. Theceramic mixture had a nominal composition of 15BaO.19Nd₂ O₃.72TiO₂.After milling for 16 hours, 7.0 gms of binder solution was added and theslurry milled for a further hour. The binder solution was a mixture of91.7% acrylic resin in MEK (5200 binder, Du Pont Co.) and 8.3% butylbenzyl pthalate plasticizer.

Ceramic tape was made from the slurry using a standard doctor-bladetechnique and then MLC's (EIA size 1206) were assembled with sixinternal electrodes and five active layers, each about 19 microns thickwhen fired. A Pd electrode paste (e.g. Du Pont 4820D) was used forprinting the electrodes. The capacitors were heated slowly to 550° C. toremove the organic binders and then the MLC's were fired at 1300° C. for2.5 hours in zirconia sand. The parts were terminated with a standard Agpaste (e.g. Du Pont 4506) for electrical testing. Average capacitancemeasured at 1 KHz was 586 pF and dissipation factor was 0.001%. Thecalculated dielectric constant was 75. TCC was -39.6 ppm per °C. at -55°C. and -35.3 ppm per °C. at 125° C., i.e. outside the requirements forCOG capacitors. Insulation resistance averaged 11,000 ohm.farads at 25°C. but was only 8 ohm.farads at 125° C., this latter value being belowCOG requirements.

EXAMPLE 2

Capacitors were made in a similar manner to those in Example 1 exceptthat the amount of barium titanate was reduced from 9.28 to 7.05 gms(i.e. 24.0%). Capacitance was 627 pF, dissipation factor was <0.001% andthe calculated dielectric constant was 72. TCC was -43.6 ppm per °C. at-55° C. and -34.0 ppm per °C. at 125° C., again outside the limits forCOG capacitors. Insulation resistance was 15,000 ohm.farads at 25° C.and averaged 10 ohm farads at 125° C., again below the requirements at125° C.

EXAMPLE 3

Neodymium titanate was made by a process similar to that described inExample 1 except that 178.9 g (0.527 mole) of neodymium acetatetetrahydrate was used instead of 169.7 g (0.50 mole). ICP analysis ofthe dried powder before ignition loss gave 65.04% Nd₂ O₃, 27.46% TiO₂,and <0.01% K₂ O. The surface area was 271.4 M² /g.

Capacitors were made in a similar manner to those of Example 2 exceptthat only 2.55 gms of TiO₂ were used and 2.45 gms of zirconium oxidepowder were added. Also, 0.08 gms of manganese carbonate (0.22 wt %) wasincluded. Average capacitance was 484 pF, dissipation factor was 0.005%and the calculated dielectric constant was 67. TCC was -2.9 ppm per °C.at -55° C. and -5.5 ppm per °C. at 125° C., i.e. well within the COGrequirements. Insulation resistance averaged 27,000 ohm.farads at 25° C.and 59 ohm.farads at 125° C. Insulation resistance at 125° C. was stillbelow the requirements at 125° C. was not improved by lowering themanganese carbonate from an 0.08 gm addition to 0.025 gms (0.067 wt % ofthe total composition).

EXAMPLE 4

Capacitors were made in a similar manner to those of Example 3, exceptthat 8.17 gms of barium titanate was used instead of 7.05 gms, and 0.090gms of cerium oxide (0.24 wt %) was added instead of the manganesecarbonate. Average capacitance was 598 pF, dissipation factor was 0.007%and the calculated dielectric constant was 74. TCC averaged -7.0 to -7.1ppm per °C. from -55° C. to 125° C., again well within the COGrequirements. Insulation resistance was 15,000 ohm.farads at 25° C. andwas 340 ohm.farads at 125° C. Thus, the addition of cerium oxide wasfound to provide good insulation resistance at 125° C., well within theCOG requirements.

EXAMPLE 5

A composition similar to that described in Example 4 was made byco-precipitation by the following method. The nominal composition was(in wt %) 44.44% Nd₂ O₃, 34.83% TiO₂, 14.08% BaO, 6.42% ZrO₂, and 0.24%CeO₂. The composition in moles is included in Table 1. Glacial aceticacid (20.0g) and 32.0 g (0.3126 mole) of 88% lactic acid were charged toa 500 ml flask under a nitrogen atmosphere and the solution heated to55°-65° C. Zirconium n-propoxide (24.3 g, 19.55% Zr, 0.0521 mole),purchased from Huls America Inc., Piscataway, N.J., was added drop-wiseover about 15 mins. while agitating the reaction mixture. Ammoniumhydroxide solution (42.7 g, 30% NH₄ OH, 0.7329 mole) was added drop-wiseto the pasty, white slurry at 55° to 65° C. over about 15 minutes. Themixture was allowed to agitate for about 30 minutes to give a clearbright yellow solution. Tyzor®-LA (253.1 g, 0.439 mole) was added andthe resulting solution allowed to agitate at 50° C. for about 30minutes. Neodymium nitrate solution (156.8 g, 28.35% Nd₂ O₃, 0.1321mole), purchased from Rhone-Poulenc, Princeton, N.J., was added and theresulting solution allowed to agitate at 45° C. for about 15 minutes.Cerium nitrate solution (0.83 g, 27.77% CeO₂, 0.0013 mole) was added andthe violet to purple solution warmed to 80°-85° C.

Using a procedure similar to that described in Example 1, the solutionof chelated metals described above was allowed to react with a hot (80°to 85° C.) solution of 24.7 g (0.09458 mole) barium nitrate and 258 g,87% KOH (4.0 moles) of potassium hydroxide in 1500 ml of de-ionizedde-gassed water. An amount (about 6%) of the total available solution ofbarium nitrate and potassium hydroxide solution was pumped through thejet-mixer in advance of the solution of chelated metals. The remainderof the solution of barium nitrate and potassium nitrate was pumpedsimultaneously with the hot solution of the chelated metals over about45 seconds through the jet mixer into 400 ml of de-ionized watercontaining 5 g of Igepal® CO-890. The slurry was heated under reflux(98° C.) for 8 hours. After cooling to 25° C., the light blue slurry wasfiltered and washed with 37 liters of de-ionized water. The filter cakewas dried in a vacuum oven (120° C.) and ground to give 107.7 g of lightblue powder with a surface area of 309.8 M² /g. The composition obtainedby ICP analysis was 37.78% Nd₂ O₃, 9.84% BaO, 29.53% TiO₂, 5.48% ZrO₂,0.618% CeO₂, and <0.01% K₂ O. The ignition loss was 10.57%.

The precipitated powder was calcined at 1000° C. for 5 hours and thenwas made into capacitors by a method similar to that described inExample 1, except that a phosphate ester surfactant was used (0.5% ofthe powder weight) in the slurry instead of the AB1015 surfactant. Also,the capacitors had 8 active layers instead of 5. Average capacitance was1091 pF, dissipation factor was 0.007%, and the calculated dielectricconstant was 72. TCC was between +94.9 and +97.5 ppm per °C. from -55°to 125° C., i.e. much more positive than allowed for COG capacitors. Itwas concluded that incorporation of the zirconium oxide in thecomposition by co-precipitation had increased its effectiveness and ledto over adjustment of the TCC. Insulation resistance averaged 10,500 at25° C. and 400 ohm.farads at 125° C., well within COG requirements.

EXAMPLE 6

A co-precipitated powder was made with the following nominal compositionby weight: 45.12% Nd₂ O₃, 14.30% BaO, 38.18% TiO₂, 2.17% ZrO₂, and 0.23%CeO₂. The composition in moles is included in Table 1. The powder wasmade in the following manner. Glacial acetic acid (400 g, 6.660 moles)and 662.6 g (6.252 moles) of 85% lactic acid were charged to a 5 literflask under a nitrogen atmosphere and the solution heated to 55° to 65°C. Zirconium n-propoxide (486.2 g, 19.55% Zr, 1.042 moles) was addeddrop-wise at 55° to 65° C. over about 30 minutes while agitating thereaction mixture. Ammonium hydroxide solution (846.2 g, 30% NH₄ OH,14.66 moles) was added drop-wise to the white pasty slurry at 55° to 65°C. over about 30 minutes. The mixture was allowed to agitate for about30 minutes. The resulting solution (2387.1 g) was clarified throughSuper Cel (filter aid) to give 2210.4 g of a clear light yellow solutionof the chelated zirconium. The solution was shown by ICP analysis tocontain 4.37% Zr. A portion of the chelated zirconium (36.3 g, 0.01737mole) was added to 273.3 g (0.4706 mole) of Tyzor®-LA in a 1 literround-bottom flask under a nitrogen atmosphere. Neodymium nitratesolution (156.8 g, 28.35% Nd₂ O₃, 0.1321 mole) was added to the charge,followed by 0.825 g, 27.77% CeO₂, (0.00134 mole) cerium nitratesolution. The resulting violet to purple solution was warmed at 80° to85° C.

Using the procedure described in Example 1, the solution of the chelatedtitanium, zirconium, neodymium and cerium was allowed to react with ahot (80° to 85° C.) solution of 24.7 g (0.09458 mole) of barium nitrateand 258 g, 87% KOH (4.0 moles) of potassium hydroxide in 1500 ml ofde-ionized and de-gassed water. An amount (about 7%) of the totalavailable solution of potassium hydroxide and barium nitrate was pumpedthrough the jet-mixer in advance of the solution of chelated metals.

The remainder of the solution of potassium hydroxide and barium nitratewas pumped simultaneously with the hot solution of the chelated metalsover about 1 minute through the jet mixer into 400 g of de-ionized watercontaining 5 g of Igepal® CO-890. The light blue slurry was heated underreflux (96° C.) for 8 hours. After cooling to 25° C., the light blueslurry was filtered and the cake washed with 40 liters of de-ionizedwater. The filtered cake was dried in a vacuum oven at 120° C. andground to give 104.5 g of a light blue powder with surface area of 271.8M² /g. The composition obtained by ICP analysis (by weight) was 36.50%Nd₂ O₃, 34.10% TiO₂, 1.86% ZrO₂, 0.274% CeO₂ and 0.023% K₂ O. BaO wasnot determined.

Capacitors were made as in Example 5 except that this co-precipitatedpowder with a lower zirconium level was used and the MLC's had 5 activelayers instead of 8. Capacitance was 761 pF, dissipation factor was0.019% and the calculated dielectric constant was 80. TCC was betterthan -20.8 ppm per °C. from -55° to 125° C., i.e. within the COGrequirements. Insulation resistance was 1700 ohm.farads at 25° C. and290 ohm.farads at 125° C., within the requirements for COG capacitors.

                  TABLE 1                                                         ______________________________________                                        Mole %                                                                        Example                                                                              BaO     Nd.sub.2 O.sub.3                                                                      TiO.sub.2                                                                           ZrO.sub.2                                                                           CeO.sub.2                                                                            MnO.sub.2                           ______________________________________                                        1      14.16   17.94   67.90 --    --     --                                  2      11.54   19.25   69.21 --    --     --                                  3      11.44   19.09   61.67 7.54  --     0.26                                4      12.80   18.43   61.30 7.28  0.19   --                                  5      12.87   18.52   61.11 7.30  0.20   --                                  6      12.87   18.52   65.98 2.44  0.20   --                                  ______________________________________                                    

We claim:
 1. A composition of a COG densified dielectric body,composition consisting essentially of:(a) 60.0-70.0 mol % TiO₂ ; (b)14.3-20.0 mol % Nd₂ O₃ ; (c) 11.0-16.7 mol % BaO; (d) 1.0-8.0 mol % ZrO₂; and (e) 0.05-0.30 mol % CeO₂.
 2. The composition of claim 1 wherein(a) through (e) are chemically co-precipitated then calcined to form thecomposition.
 3. The composition of claim 2 consisting essentially of(a)64.0-67.0 mol % TiO₂ ; (b) 18.0-19.0 mole % Nd₂ O₃ ; (c) 12.8-13.0 mol %BaO; (d) 1.5-3.0 mol % ZrO₂ ; and (e) 0.15-0.25 mol % CeO₂.
 4. Thecomposition of claim 1 further comprising an organic medium containing asolution of volatile organic solvent and organic polymeric binder.
 5. Adielectric sheet comprising a cast layer of the composition of claim 4which has been heated to remove volatile organic medium.
 6. A dielectricceramic layer comprising the sheet of claim 5 which has been fired tovolatilize the organic medium therefrom and to densify the inorganiccomponents by sintering.
 7. A capacitor comprising a plurality of thedielectric ceramic layers of claim 6, and at least two metal electrodeswhich are separated from each other by at least one said dielectricceramic layer, the assemblage having been fired at a temperature above1240° C. to volatilize organic medium, densify the inorganic materialsin the dielectric sheets and sinter the metal electrodes.